Above-threshold ionization of Kr atoms in an infinite sequence of circularly polarized few-cycle pulses

Above-threshold ionization of Kr atoms in an infinite sequence of circularly polarized few-cycle pulses is studied in the frame of a nonperturbative scattering theory. The photoelectron angular distributions (PADs) in various pulse lengths are obtained. Our study shows that the PADs in circularly polarized few-cycle pulses are not isotropic and the photoelectron rates in a pair of two opposite directions are not always equal to each other. This inversion asymmetry is due to a multichannel transition where the different channels are characterized by different combinations of absorbed-photon numbers in the ionization process. The PADs are symmetric about an axis related to the carrier-envelope (CE) phase. Our study also shows that the position of the maximal emission is related to the CE phase and the pulse length of the short pulses, which makes it possible to control the motion of the ejected photoelectrons by varying the pulses